This invention relates generally to refrigerants, and more particularly to a halocarbon/hydrocarbon refrigerant blend.
Refrigeration systems have been in widespread use for decades. These systems have a wide variety of uses, such as comfort cooling, household refrigeration, automobile air conditioning, commercial freezer cooling, and the like. Such systems work on the basic premise that a fluid, known as a refrigerant, picks up heat from an area to be refrigerated, and disposes of the heat in an area not affected by an increase in heat.
Refrigeration processes are well known in the art. Typically, such processes encompass a changing state of the fluid from a liquid to a vapor, and vapor to liquid, which change of state allows for the rapid removal of heat from the area to be refrigerated. Different types of refrigeration systems use different refrigerants having properties designed to enable the given system to approach maximum performance.
R-12 (dichlorodifluormethane) has long been the refrigerant of choice for uses ranging from domestic and commercial refrigeration, to automobile air conditioners. However, the international community has now come to recognize that chlorofluorocarbon refrigerants (CFC's), such as R-12, have an adverse effect on the earth's protective ozone layer. International agreements, such as the Montreal Protocol, have called for a phase out of these CFC's. As a result, the scientific community faced the task of developing suitable replacements for those CFC's. To date, much time and effort has been expended to find such suitable replacements.
Several low ozone-depleting refrigerants have been promoted as replacements for CFC refrigerants. Perhaps the most widely used replacement refrigerant is 1,1,1,2-tetrafluoroethane (R-134a). Nearly all new automobile air conditioners, fresh food storage compartments and like devices are now being manufactured to use R-134a as the refrigerating fluid. R-134a is non-ozone-depleting, non-flammable and nontoxic. However, the use of R-134a necessitates major changes in most refrigeration systems. For example, the naphthenic lubricating oils typically used with R-12 are not compatible with R-134a. Thus, it is necessary to completely drain these oils from systems previously using R-12, and replace the oil with an oil more compatible with R-134a. In addition, some equipment used in existing air conditioning systems, such as the hoses used in automobile air conditioning systems, is not compatible with R-134a, thus necessitating significant overhaul and replacement of portions of these air conditioning systems. A further drawback to the use of R-134a as a replacement for R-12 is that the thermodynamic properties of R-134a are generally inferior to those of R-12. As a result, refrigeration systems using R-134a require more electrical consumption. In addition, in order to obtain the same level of cooling in an automobile air conditioning system using R-134a when compared to a system using R-12, the additional work required of the engine with the R-134a reduces the gas mileage compared to that obtained in an otherwise similar automobile under similar conditions, but utilizing R-12 refrigerant.
Several refrigerant blends have also been promoted as substitutes for R-12. A ternary halocarbon blend consisting essentially of R-22, R-124 and R-142b is described in U.S. Pat. No. 5,188,749. A ternary halocarbon blend of R-22, R-114 and R-152a is described in U.S. Pat. No. 4,810,403. However, use of the blended compositions described in these patents requires that the oil normally found in an existing refrigeration system be replaced with an oil specifically designed for use with that refrigerant blend, due to the immiscibility of the oil normally used in the refrigeration systems with the replacement refrigerant. In addition, even when the replacement oil is used, the temperature range in which the oil is miscible with the refrigerant may be narrower than that when R-12 is used. As a result, these blends are generally only useful in applications where the operating temperatures are within these, sometimes narrow, ranges of miscibility. If the particular refrigeration application includes operating temperatures outside the range of miscibility of the particular oil in the refrigerant, the compressor may become damaged due to insufficient lubrication.
U.S. Pat. No. 4,482,465 teaches blends of halocarbon/hydrocarbon refrigerants, and provides direction how to blend these refrigerants to provide a composition having reduced flammability. However, this patent does not address the issue of oil miscibility.
U.S. Pat. No. 5,151,207 teaches a blend of the halocarbons R-22 and R-142b, with the addition of a minor hydrocarbon component, in this case isobutane. Although this refrigerant blend is miscible with oils commonly found in refrigeration systems, the use of relatively large amounts of the flammable halocarbon R-142b in connection with the hydrocarbon isobutane may cause the refrigerant blend to become weakly flammable if about sixty percent or more of the blend leaks from a refrigeration system or container. The flammability of this refrigerant presently precludes its use in automobile air conditioning systems.
Accordingly, a need exists for a refrigerant that may be employed as a direct replacement for CFC's such as R-12. The replacement refrigerant should be compatible with existing refrigerant equipment, and miscible with lubricating oils presently used in such equipment throughout a wide range of operating temperatures. In addition, the replacement refrigerant should be nonflammable, not only as manufactured but also after significant refrigerant loss has occurred from the system due to system damage or system component failure. Further, the refrigerant composition should have thermodynamic properties comparable to R-12.